EGFR variant III (EGFRvIII), a tumor specific mutant of EGFR, is a product of genomic rearrangement which is often associated with wild-type EGFR gene amplification. EGFRvIII is formed by an in-frame deletion of exons 2-7, leading to deletion of 267 amino acids with a glycine substitution at the junction. The truncated receptor loses its ability to bind ligands but acquires constitutive kinase activity. Interestingly, EGFRvIII frequently co-expresses with full length wild-type EGFR in the same tumor cells. Moreover, EGFRvIII expressing cells exhibit increased proliferation, invasion, angiogenesis and resistance to apoptosis.
EGFRvIII is most often found in glioblastoma multiforme (GBM). It is estimated that 25-35% of GBM carries this truncated receptor. Moreover, its expression often reflects a more aggressive phenotype and poor prognosis. Besides GBM, expression of EGFRvIII has also been reported in other solid tumors such as non-small cell lung cancer, head and neck cancer, breast cancer, ovarian cancer and prostate cancer. In contrast, EGFRvIII is not expressed in healthy tissues. The lack of expression in normal tissues makes EGFRvIII an ideal target for developing tumor specific targeted therapy. To date, there has not been any FDA approved monoclonal antibody (e.g., monospecific or bispecific) against EGFRvIII identified with high affinity, high specificity, and high potency in treating cancers such as GBM. Accordingly, there remains a need for antibodies (e.g., monospecific or bispecific) treating cancers such as GBM with improved efficacy and safety profile, and suitable for use with human patients.